PRODUCTION AND REGULATION OF POLYGALACTURONASE ISOZYMES IN CANADIAN ISOLATES OF LEPTOSPHAERIA-MACULANS DIFFERING IN VIRULENCE

The polygalacturonase (PG) isozymes produced by weakly virulent and hi ghly virulent Canadian isolates of Leptosphaeria maculans that cause b lackleg on canola, were examined. PG zymograms as determined by isoele ctric point and molecular weight were distinctive between the highly v irulent and weakly virulent types and could be used to differentiate t he geographic origin of isolates within both virulence types. Highly v irulent isolates produced PG isozymes of greater mobility in polyacryl amide gels than those of the weakly virulent isolates. Highly virulent isolates produced fewer PG isozymes with only acidic isoelectric poin ts compared to weakly virulent isolates which produced many isozymes w ith either acidic or basic isoelectric points. Production of most PC i sozymes was induced by polygalacturonic acid and was not repressed by glucose, and some isozymes were produced at basal levels without induc tion, suggesting that regulation of isozymes may have an effect on the ir activity in plant tissue. The characteristics of specific PG isozym es may affect their activity in the plant and the virulence of L. macu lans isolates to their host. PG zymograms also will be useful as chara cteristics for analyzing the diversity of L. maculans populations.